Improved DC Gun Insulator Assembly

Many DOE user facilities, such as synchrotron radiation light sources and free electron lasers, require accelerating structures that can support electric fields of 10-100 MV/m, especially at the start of the accelerator chain where ceramic insulators are used for very high gradient DC guns. These insulators are difficult to manufacture, require long commissioning times, and have poor reliability. Part of the problem is that the energetic electrons bury themselves in the ceramic, causing a buildup of charge and eventual puncture of the insulation. Another problem is that large-diameter ceramics are difficult to braze reliably. In this project, a novel ceramic manufacturing process will be developed that will incorporate the bulk resistivity needed to bleed off the accumulated charge from the highly energetic electrons. A novel metal-to-ceramic seal ring design will be used to minimize tensile stresses in the vacuum joint. In Phase I, a computer model will be used to determine the optimum metal-to-ceramic vacuum seal dimensions, coating dimensions, and required resistivity gradient for a particular RF gun application; a sample ceramic material with a resistivity gradient appropriate for use as a DC gun insulator will be fabricated; and a design for a novel metal-to-ceramic vacuum seal ring will be incorporated for large diameter ceramic assemblies. Commercial Applications and other Benefits as described by the awardee: Ceramics with gradients in bulk resistivity should have a wide range of application in high voltage standoffs for electron guns in X-ray tubes and high power microwave tubes, as well as for high gradient accelerator guns.